Role of Clinical Imaging

Question 1

What is imaging

Answer 1

All tests health care staff use to see inside the body that cannot be seen or felt from the outside

Question 2

What tests are imaging tests

Answer 2

X-rays
Ultrasound
Magnetic resonance imaging (MRI)
Nuclear medicine

Question 3

Types of X-rays

Answer 3

• Plain radiography
• Computed tomography (CT)
• Contrast studies (arthrography)

Question 4

What is an X-ray

Answer 4

electromagnetic radiation produced by electrical source which passes through body tissue to degree dependent on its density

Question 5

How do we produce an X-ray

Answer 5

Electric current heats a filament cathode then electrons are emitted and strike anode
Generated x-rays exit window and beam made parallel
X-rays penetrate patient and scatter

Question 6

What system allows easy storage, access and retrieval of digital images

Answer 6

PACS
Picture Archiving & Communications System

Question 7

How is the picture produced

Answer 7

The denser the tissue fewer X-rays pass through it so
-Air allows all to pass through
-Soft tissue lets some
-Cortical Bone lets almost none

X-ray film blackened when x-rays hit it

Question 8

X-ray strengths

Answer 8

Shows things surrounded by air (black) e.g lung cancer

Show things surrounded by bone (white) e.g fractures

Show things destroying white bone e.g bone cancer

Question 9

X-ray weaknesses

Answer 9

Abnormality must be of very different density to tissue surrounding it to be seen

Pathology has similar densities to surrounding tissue and cant be seen on simple x-rays

Question 10

What are contrast studies

Answer 10

Liquids like barium or iodine (dense) can block x-rays allowing tissue outlines to be visible when in spaces between tissues

Question 11

What are Enema and Arthrogram contrast studies

Answer 11

Enema- Barium poured into cleansed colon shows sigmoid cancer

Arthrogram- Iodine rich fluid injected into shoulder joint to outline capsule

Question 12

Dangers of X-rays

Answer 12

Radiation can damage cell DNA leading to mutations, may kill cell or turn it cancerous

risk related to X-ray dose - benifit to patient must outweigh the risk

Question 13

What is Computed tomography -CT

Answer 13

Able to distinguish tissues of similar density and shows soft tissue pathology
Has superior contrast resolution compared to radiograph

Question 14

Where are X-rays fired from in CT

Answer 14

All round the body
to be processed and produce a cross- sectional picture with no superimposition

Question 15

Why isn’t CT just used instead of X-ray

Answer 15

As it gives larger doses of ionising radiation
&
Very similar density soft tissues not distinguishable e.g. pelvic organs, muscles and tendons, areas of the brain

Question 16

What can ultrasound differentiate that CT cant

Answer 16

Pelvic organs
Muscles and tendons

Question 17

How ultrasound works

Answer 17

piezoelectric crystals can convert electrical energy to acoustic energy

these crystals are housed in a transducer which has an electrical supply

the transducer produces pulses of sound waves alternatively transmitting then listening for reflected sound

Question 18

How is an ultrasound image obtained

Answer 18

returning acoustic energy is converted back into an electrical impulse and fed into a computer

computer ‘knows’ where the sound has come from by the time taken for it to return to the transducer

Uses this to make a cross-sectional picture of soft tissue

Question 19

What makes a good ultrasound

Answer 19

1. Tissue allowing sound transmission
2. Good skin- transducer contact
3. slim patients
4. Tissues with different acoustic properties

Question 20

What makes a bad ultrasound

Answer 20

1. Tissues preventing sound transmission (gas & bone)
2. Poor skin-transducer contact
   3.Obese patients
3. Tissues with identical acoustic properties

Question 21

Ultrasound strengths

Answer 21

High spatial resolution useful in MSK imaging of soft tissue

Fluids transmit ultrasound whilst solids reflet it

Abnormal fluid collections seen

Question 22

Ultrasound weaknesses

Answer 22

Bone blocks ultrasound so brain not seen

Gas blocks US so windy patients difficult to assess

Question 23

How does MRI work

Answer 23

the scanner produces a burst of radio signal (RF pulse), which energises the body’s protons

the scanner waits

the scanner listens for a return signal, produced by the protons

the amount of signal produced depends on the molecular environment of these protons

using the returned signal, the scanner’s computer performs some amazingly complex calculations and creates an image

Question 24

What problems have been described with MRI

Answer 24

Frostbite and thermal burns
Deafness
Surgical & non-surgical materials disturbed e.g. pacemakers, valves

Question 25

Why is MRI not liked by patients

Answer 25

Very time consuming
spine= 25-40mins
knee= 25 mins
ankle= 30 mins Both= 1 hour

Question 26

MRI strengths

Answer 26

Provides most complete brain assessment
Provides excellent detail of spinal canal disease
Interior of joints images

Question 27

MRI weaknesses

Answer 27

Is very expensive
Harms some patients so contraindicated
Claustrophobic

Question 28

What is the role of imaging

Answer 28

To make or confirm a diagnosis

To help narrow a differential diagnosis

To ‘STAGE’ an known disease, eg cancer to inform treatment

To monitor the effects of treatment and follow up a known disease

To aid intervention/deliver treatment eg image guided procedures or interventional radiology